The present invention relates to a method of precision calibration of magnification of a scanning microscopes with the use of test diffraction grating.
Methods of precision calibration of a magnification of scanning microscopes with the use of test diffraction gratings are known. In the existing methods a test object is positioned and oriented on a microscope stage, and corresponding part of the test objects is scanned, with subsequent processing of the thusly obtained data. It is believed that the existing methods can be further improved.
Accordingly, it is an object of the present invention to provide method of precision calibration of magnification of a scanning microscopes with the use of test diffraction grating.
In keeping with these objects and with others which will become apparent hereinafter, one feature of present invention resides, briefly stated, in a method of precision calibration of magnification of scanning microscopes with the use of a test diffraction grating, comprising the steps of positioning and orientation of a test object on a stage of microscope so that strips of a test diffraction grating are perpendicular to a direction along which a calibration is performed; scanning of a selected portion of the test object along axes X and Y; measuring values of a signal S versus coordinates x and y in a plane of scanning and storing of said values S (x, y) in a digital form as a two-dimensional digital array; transforming the two-dimensional array of signals S(x, y) into a two-dimensional array S (u, v) by turning of the axes so that a direction of a new axis u is perpendicular to the strips of the grating and a direction of a new axis v coincides with the strips of the grating; line-by-line mathematical processing of the array S (u, v) including for each line S(u) approximating of an array of discrete values S (u) with a periodical analytical function
Y(x)=A* sin(B*xxe2x88x92c)+D 
wherein A, B, C, D are the empiric constants whose values are selected in accordance with a best correspondence between an analytical curve and the array of S(u), and determining a pitch Tv of the analytical function Y(x) in accordance with a formula:
Tv=2*xcfx80/B, 
wherein Tv is a value of the pitch in pixels, B is a value of the empirical constant B obtained in a previous step and corresponding to a best approximation of the array S(u) to the analytical function; transferring to a next line S(u) with a new coordinate v and performing the same processing: approximation, pitch determination; performing standard statistical processing of sets of values Tv corresponding to various lines v by calculating of an average value of the pitch T for all lines; and calculating a magnification Mu in accordance with the selected direction u in correspondence with the formula:       M    U    =            T      ·      L                      T        0            ·      N      
wherein L is a width of a medium of the image in a direction of calibration, To is an independently attested value of a pitch of the test object in absolute units, N is a number of pixels in the line along the direction u.
When the method is performed in accordance with the present invention, the method is simpler which requires less expense for corresponding programming and it is more accurate than the existing methods.
The novel features which are considered as characteristic for the present invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.